1. Field of the Invention
The present invention relates to a polishing method and polishing device, and more particularly to a polishing method and polishing device using a polishing tape having abrasive grains fixed to the front surface thereof or asperities formed on the front surface thereof.
2. Description of the Related Art
In the fabrication of semiconductor devices on a wafer, various processing steps such as film deposition, etching, and planarization are repeated. In the past, it is sufficient that the condition of processing in each step be uniform within the wafer. However, it has become difficult to maintain the uniformity within the wafer in relation to an increase in diameter of the wafer. In particular, it has become difficult to control the processing of the end surface of the wafer as maintaining the uniformity within the wafer.
Further, a metal material such as copper (Cu) having an effect on transistor characteristics has been used for wiring on the wafer. For example, in the fabrication of semiconductor devices using a silicon (Si) wafer, it is necessary to protect the lower surface and end surface of the wafer in the processing step for Cu wiring on the wafer, so that the processing step has become increasingly complicated. Due to the complication of the processing step, it is very difficult to control particles on the end surface of the wafer present between the upper and lower surfaces of the wafer. Accordingly, in recent years, the end surface of the wafer has been polished in the process of forming semiconductor devices to thereby suppress the generation of foreign matter from the end surface of the wafer (see Japanese Patent Laid-Open No. 2001-345294, for example).
As a method of polishing the end surface of a wafer, it is known that a polishing cloth is pressed on the end surface of the wafer being rotated in the condition where a polishing slurry containing abrasive grains is supplied onto the upper surface of the wafer (see Japanese Patent Laid-Open No. 2003-209075, for example) . According to this method, the end surface of the wafer is polished in the condition where the abrasive grains are not fixed to the polishing cloth, so that polishing marks by the abrasive grains are hardly left on the end surface of the wafer. However, after the polishing, it is necessary to perform a cleaning step using a cleaning liquid having a strong cleaning power, so as to remove the abrasive grains from the wafer. This cleaning step is difficult to perform in the condition where semiconductor devices are mounted on the wafer, so that the processing steps to which such cleaning is applicable are limited.
There has been reported a method of polishing the end surface of a wafer by using a polishing tape (polishing film) having abrasive grains fixed to the front surface thereof (see Japanese Patent Laid-Open No. 2003-163188, for example). An example of this polishing method will now be described with reference to FIGS. 8A and 8B. As shown in FIG. 8A, reference numeral 40 generally denotes a polishing tape composed of a film base 41 and an adhesive layer 42 formed on the front surface of the film base 41. Adhesive grains 43 are fixed to the front surface of the adhesive layer 42. The polishing tape 40 is pressed on the end surface of a rotating wafer W so that the abrasive grains 43 cut into the end surface of the wafer W. In this polishing method, pure water is generally used as a polishing liquid rather than the polishing slurry containing abrasive grains. Accordingly, after the polishing, it is not necessary to perform strong cleaning, so that this polishing method can be easily applied to the fabrication of semiconductor devices.